1. Field of the Invention
This invention generally relates to an electrochemical battery and, more particularly, to an alkali-ion battery using a cathode formed from a thick transition metal cyanometallate (TMCM) sheet.
2. Description of the Related Art
The demand continues to emerge for an economic means of storing the energy generated from renewable, but intermittent, solar and wind power sources. This energy transformational technology is expected to enable the large scale integration of renewable energy and to dramatically increase power generation and transmission efficiency. Rechargeable room-temperature batteries have several advantages for this application, including scale flexibility, economic maintenance, and energy-storage efficiency, as compared to other energy-storage technologies such as fly wheels, pumped water, compressed air, and high-temperature sodium/sulfur batteries. Although lithium-ion batteries are a well-developed successful product, the high demand for lithium and its limited reserves have led to a surge in its cost, which hinders the application of lithium-ion batteries on a large scale. Therefore, a low-cost rechargeable battery is urgently needed as an alternative to expensive lithium-ion batteries.
Sodium/potassium-ion batteries have recently received a great deal of attention because the reserves of sodium/potassium in the crust of the earth are much higher than lithium. This abundance makes possible the development of low cost batteries for electrical energy storage (EES). However, it has proved impractical to copy the structures of Li+-host compounds to Na+ or K+-host compounds. Sodium/potassium ions are much larger than lithium ions and they severely distort the structures of the Li+-host compounds. Thus, for the development of sodium/potassium-ion batteries it is important to develop new Na+/K+-host materials with large interstitial space in which sodium/potassium-ions can easily and reversibly move. Transition metal cyanometallate (TMCM) materials with large interstitial space have been investigated as cathode materials for rechargeable lithium-ion batteries [1, 2], sodium-ion batteries [3, 4], and potassium-ion batteries [5].
The most widely used method to make an electrode for lithium ion batteries, sodium ion batteries, and supercapacitors is a coating process. An organic solvent or an aqueous solution is used to dissolve a binder, and the binder solution is then mixed with an active material powder and conductive additives to form a slurry. The slurry is then coated on a current collector. The current collect with the coating layer is dried and calendared to a desired porosity and thickness. Generally, the thickness of the active material is around 50 to 100 microns (μm) for electrode made by coating method [6]. Delamination or cracks occur when the thickness of the coated electrode increases beyond this limit. The capacity of an electrode made from any given active material could be improved by increasing the electrode thickness [7].
It would be advantageous if the thicknesses of the TMCM active material formed on a cathode current collector could be increased.
It would be advantageous if the number of cells, and therefore overall size, of a TMCM cathode battery could be decreased, while maintaining the same capacity.
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[3] Y. Lu, L. Wang, J. Cheng, J. B. Goodenough, “Prussian blue: a new framework for sodium batteries”, Chemistry Communication, 48(2012)6544-6546.
[4]L. Wang, Y. Lu, J. Liu, M. Xu, J. Cheng, D. Zhang, J. B. Goodenough, “A superior low-cost cathode for a Na-ion battery”, Angew. Chem. Int. Ed., 52(2013)1964-1967.
[5] A. Eftekhari, “Potassium secondary cell based on Prussian blue cathode”, J. Power Sources, 126 (2004) 221-228
6] G. Yang, K. Song and S. Joo, “Ultra-thick Li-ion battery electrodes using different cell size of metal foam current collectors” RSC Adv., 2015, 5, 16702.
[7] R. Zhao, J. Liu, J. Gu, “The effects of electrode thickness on the electrochemical and thermal characteristics of lithium ion battery”, Applied Energy 139 (2015) 220-229.